The invention relates generally to packaging for microelectromechanical systems (MEMS).
MEMS devices include fragile structures such as thin flexible membranes or rigid moving parts. The fragile structures can easily be damaged mechanically or by exposure to moisture. Protection of the fragile structures has posed a problem both for use of MEMS devices and for multichip module (MCM) packaging of MEMS devices.
Most MEMS devices are packaged in an xe2x80x9cunreleasedxe2x80x9d state and require a xe2x80x9creleasexe2x80x9d etch prior to operational use. The release process often includes removing selected materials to create three-dimensional structures and, in some cases, to allow physical movement. Released MEMS devices are typically very fragile and require special handling. MCM packaging of unreleased MEMS devices requires that the package materials be compatible with the MEMS release procedures, and protective enclosures typically are not provided as part of the package.
Another challenge when fabricating systems with MEMS devices involves monolithic integration of MEMS devices with associated interface electronics when such integration requires the MEMS device fabrication to be compatible with standard complementary metal oxide semiconductor (CMOS) integrated circuit (IC) chip fabrication processes.
It would be desirable to provide an MCM packaging method capable of reliably packaging released MEMS devices. Packaging released MEMS devices would permit the MEMS devices to be pretested for functionality. It would further be beneficial for the packaging method to provided an enclosure to protect fragile MEMS structures from mechanical and/or chemical attack.
It would further be desirable to use the very small form factor (footprint) of the chip-on-flex type packaging to permit integration of CMOS IC chips with MEMS devices such that the resulting form factor is comparable to monolithic integrated devices. Such packaging would provide more flexibility in MEMS system design.
Briefly, in accordance with one embodiment of the present invention, a method for packaging a microelectromechanical system (MEMS) device comprises: using a partially-cured adhesive to attach a release sheet to a MEMS package flexible layer; providing a cavity extending through the release sheet and at least partially through the MEMS package flexible layer; removing the release sheet; and attaching the MEMS device to the MEMS package flexible layer with a MEMS structure of the MEMS device being positioned within the cavity.